Residents in Coonamble in central-western New South Wales are anxiously waiting for flood waters to peak this morning amid fears the town's levee will be breached.

The State Emergency Service says the Castlereagh River is at 4.9 metres at Coonamble and continuing to rise steadily.

The levee is holding, but the waters are due to peak at 5.5 metres - classified as a major flood - around noon (AEDT) today.

SES spokesman Phil Campbell says about 1,200 residents have been evacuated since yesterday and an evacuation centre has been set up at the Coonamble Bowling Club.

About 100 residents, however, are refusing to leave their homes.

"Due to some uncertainty about the ability of the levee to withstand a flood of this particular size, the decision was made to move approximately 1,200 people," he said.

SES spokeswoman Erin Pogmore says volunteers are checking gauges on the river every 30 minutes to see whether the town's levee will hold.

"The concern is that it may not have the ability to keep the water out at the level that's being predicted at 5.5 (metres)," Ms Pogmore said.

"The possible breach of that would introduce high-velocity flash-flood water into that area, so that's what the concern is that it will breach in one part of the levee, not the whole levee collapsing."

Fine conditions forecast for today, however, are expected to assist emergency crews operations.

Ms Pogmore says crews from across the state are on stand-by.

"We're expecting that the conditions today are very similar to those that we had yesterday, so a nice sunny day.

"It does make things easier when we've got volunteers out in the field. It's easier for them to get out and about when visibility's good."

The mayor of Coonamble, Tim Horan, says one positive from the flooding could be extra funding from the State Government to improve the town's levee.

"There has been some concerns over the years with the conditions and a lot of weak points within the levee and we've been seeking assistance, government assistance to try and rectify the problem," Mr Horan said.

"We haven't been successful to date, so hopefully if anything comes out of this we might be able to get some funding to assist with the levee."

Meanwhile, emergency crews are working against the clock to airlift livestock from isolated properties in Brewarrina before the next wave of floodwaters arrive.

Namoi SES region controller Kath Cain has moved into the area to assist in the operation, which has 15 helicopters working around the clock moving mainly sheep to higher ground.